The present invention relates to a liquid extreme pressure additive for use in lubricating compositions.
A variety of additives are used in lubricants to substantially improve performance. For example, extreme pressure additives are routinely incorporated into an untreated lubricating composition (e.g., greases) to significantly improve performance. Extreme pressure additives are believed to produce a film on the surface of a metal which can both increase the load carrying capacity of lubricant, and protects the metal surface under high load conditions from deterioration due to wear, welding, and abrasion.
Lead naphthenates and lead dialkyldithiocarbamates were frequently used as additives to improve the EP performance of greases. However, lead is a heavy metal which is considered poisonous in all forms. As an alternative, metal additives (such as antimony, zinc, and bismuth) have been used as a replacement for lead. However, these heavy metals still provide environmental concerns regarding their use. Accordingly, it has long been a goal in the art to develop non-metal lubricating materials to replace heavy metal additives while providing acceptable extreme pressure performance.
The effectiveness of potential extreme pressure additives is conventionally ascertained by the 4-Ball Weld Test (ASTM D-2596) and the Timken Load Test (ASTM D-2509). An ideal candidate compound should exhibit good results in both tests since each test is directed to different extreme pressure properties.
Some 2,5-dimercapto-1,3,4-thiadiazole (DMTD) derivatives can be effective as anti-wear additives in lubricants. Examples of DMTD derivatives useful as anti-wear additives include: the monosulfide and disulfide dimers of DMTD as disclosed in U.S. Pat. Nos. 4,517,103 and 5,194,621; maleate adducts of DMTD as disclosed in U.S. Pat. Nos. 5,102,568, 5,055,584 and 5,138,065; and mono-alkylated and thioacteal derivatives as disclosed in U.S. Pat. No. 5,849,925.
International Application PCT/US 2005/045559, published as WO 2006/066068A2 on Jun. 22, 2006, discloses a composition comprising an oil of lubricating viscosity and a mixture of at least one dimercaptothiadiazole polymer or derivative thereof and at least one unsaturated carboxylic acid.
U.S. Pat. No. 6,489,484, Karol, et al., Dec. 3, 2002, discloses thiadiazole-poly(ether)glycol reaction products and adducts useful as extreme pressure additives.
U.S. Pat. No. 6,365,557, Karol, et al., Apr. 2, 2002, discloses 2,5-dimercapto-1,3,4-thiadiazole dimer-poly(ether)glycol reaction products and adducts useful as extreme pressure additives.
There are some DMTD-based derivatives that can provide acceptable 4-Ball Weld properties. Unfortunately, these same derivatives generally exhibit poor Timken Load performance since the DMTD derivatives do not generally provide Timken Loads levels greater than 35 pounds. As a result, commercialization of DMTD derivatives as extreme pressure additives has been limited. The use of some DMTD derivatives are also limited due to their insolubility in oil, making it difficult to utilize them in oil-based lubricating compositions.
In view of the above, there exists a need in the art for DMTD derivatives that provide both adequate 4-Ball Weld and Timken Load properties and which can be easily used in oil-based lubricating compositions. Accordingly, it is an object of the present invention to provide DMTD derivatives that provide adequate 4-Ball Weld and Timken Load properties, which will allow for the effective utilization of DMTD derivatives as extreme pressure additives.